The present invention relates to synchronisation between at least two signals. More specifically, the invention relates to a method, and a corresponding device, of synchronising a first signal, e.g. an audio signal, and a second signal, e.g. a video signal. The invention also relates to a method, and a corresponding device, of enabling synchronisation of an audio signal and a video signal. Further, the invention relates to a computer readable medium having stored thereon instructions for causing one or more processing units to execute the method according to the invention.
Synchronisation of a video stream with a corresponding audio stream is a difficult problem which has received a lot of attention. Many solutions to this problem have been proposed and implemented. Most of these solutions require manual synchronisation by a skilled operator. Typically the operator looks for visual clues within the picture to determine if the sound heard corresponds to the picture and that they are indeed synchronous. The problem becomes much harder when the synchronisation needs to be done automatically. This is a problem that is becoming more and more relevant, as processing and distribution of audio and video signals are becoming ever more complicated, both inside and outside a studio environment. An example of the latter is the following: A consumer records a movie with his video recorder. He would like to view it with the original sound-track. Therefore he buys the original soundtrack, which, for example, is streamed to him over the Internet. Now the audio and the video need to be synchronised automatically e.g. in/by his video recorder or another synchronisation device.
One previous system that would allow the automatic synchronisation of an audio and a video stream is marketed by Tektronix. In this system, the envelope of the audio signal is embedded by means of a watermark into the video signal. At any point in the distribution of processing chain, the actual audio envelope can be compared to the embedded one, from which the delay between the two streams can be derived. Subsequently, the delay of the audio is corrected to achieve synchronisation. However, this system requires the co-operation of the broadcaster or another distributor, because before transmission, the watermark needs to be embedded in the video. Further, this system can only associate one particular audio stream to the video. Once the envelope of an audio stream has been embedded, the system can only synchronise the video with that particular audio stream. For synchronising other audio streams, another watermark should have been embedded. Finally, the system is restricted to synchronisation between an audio stream and a video stream.